NDPR has a review of my Actuality, Possibility, and Worlds by Eric Hiddleston. I think it's quite a helpful review--the concerns about my account are powerful and interesting.
This post is a very rough bunch of responses to Hiddleston, and will not be comprehensible without reading his review.
I am inclined to endorse some version of the "externalist" way out that Hiddleston gives. I think this will damage at least one of my arguments against Platonism, the one that says that opponents of Platonism are "horribly confused" if Platonism is true. But Hiddleston is right that that's a bad argument.
I think Hiddleston doesn't give enough credit to my dogs argument against Platonism. There, I am imagining that the Platonist heaven is augmented with the necessity of there being no dogs, but all earthly stuff is unchanged. I claim in the book that nonetheless dogs would remain possible. My line of thought behind that was that dogs would remain possible, because they would remain actual, and the actual is possible, no matter what the Platonist heaven says. I think Hiddleston's Little-P = Big-P position doesn't help here.
(It occurs to me, by the way, that the Platonist could have a theory that escapes my dogs argument as it stands in the book. Here's the theory. The primitive property is mere possibility. Possibility is then defined in terms of mere possibility: a proposition is possible provided that it is either true or merely possible. But I think this version still has a problem. The original Platonic version has the puzzle of why it is that actuality implies possibility. This version doesn't have that problem. Instead it has the problem of why it is that that mere possibility implies non-actuality.)
Hiddleston also worries a lot about Euthyphro-type questions, like:
- (E1) Why should God be incapable of bringing about really impossible propositions, such as contradictory ones?
- (E2) Why should God be capable of bringing about really possible propositions?
- If, per impossibile, God or any other agent were capable of bringing about a contradictory proposition, that proposition would be possible.
- If, per impossibile, God were to command a horrendous deed, that horrendous deed would be obligatory.
I do think Hiddleston's question about what explains why God can do contradictory things is a good and difficult question, but I don't think they're quite species of the Euthyphro problem. I think I can say that there just does not exist any being with the power to bring about contradictory propositions. This is in need of no more grounding than the fact that there are no unicorns--it's just a negative existential. Is it in need of an explanation? My official line on the PSR restricts it to contingent truths. But maybe there still is an explanation of it in terms of some deep facts about the divine nature (maybe its beauty, say). Maybe Hiddleston's best bet here would be to push me in a way that Josh Rasmussen has done: I can't explain why God can't create square circles, just as the Platonist can't explain why everything that's actual is also possible, and so I don't have an advantage over the Platonist here. I don't know exactly what to say here, but I think one difference is with regard to per impossibile counterfactuals.
- If dogs existed but the Platonic heaven didn't say that they were possible, dogs would still be possible.
- If God were capable of creating a square circle, square circles would be possible.
As for (E2), I don't feel the force of that. First of all, the primary view doesn't mention God: it's quantified over all agents. So the modified question is:
- (E2b) Why should every really possible proposition be such that there is an agent who can bring it about (or, more precisely, bring about a chain of causes leading to it)?